CAUCASUS, a mountain range of Asia, wholly within the Russian empire, stretching north-west to south-east from the Strait of Kerch (between the Black Sea and Sea of Azov) to the Caspian Sea, over a length of 900 m., with a breadth varying from 30 to 140 m. In its general character and conformation the Caucasus presents a closer analogy with the Pyrenees than with the Alps. Its general uniformity of direction, its comparatively narrow width, and its well-defined limits towards both south and north are all features which it has in common with the former. The range of the Caucasus, like that of the Pyrenees, maintains for considerable distances a high average elevation, and is not cleft by deep trenches, forming natural passes across the range, such as are common in the Alps. In both ranges, too, some of the highest summits stand on spurs of the main range, not on the main range itself; as Mont Perdu and Maladetta lie south of the main backbone of the Pyrenees, so Mount Elbruz and Kasbek, Dykh-tau, Koshtan-tau, Janga-tau and Shkara—all amongst the loftiest peaks of the Caucasus—stand on a subsidiary range north of the principal range or on spurs connecting the two . On the other hand, it is interesting to compare the arrangement of the drainage waters of the Caucasus with those of the Alps . Inboth orographical systems the principal rivers start nearly all together from a central nucleus, and in both cases they radiate to opposite quarters of the compass; but whereas in the Alps the Rhone and the Rhine, flowing south-west and north-east respectively, follow longitudinal valleys, and the Aar and the Ticino, flowing north-west and south-east respectively, follow transverse valleys, in the Caucasus the streams which flow south-west and north-east, namely, the headwaters of the Rion and the Terek, travel along transverse valleys, and those of the Kura and the Kuban, flowing south-east and north-west respectively, traverse longitudinal valleys. For purposes of description it is convenient to consider the range in four sections, a western, a middle with two subsections, and an eastern.

This section, extending from the Strait of Kerch to Mount Elbruz in 42° 40' E., is over 420 m. long, and runs parallel to the north-east coast of the Black Sea and at only a short distance from it. Between the main range and the sea there intervene at least two parallel ranges separated by deep glens, and behind it a third subsidiary parallel range, likewise separated by a deep trough-like valley, and known as the Bokovoi Khrebet. All these ranges are shorn through transversely by numerous glens and gorges, and, the rainfall being heavy and the exposure favourable, they are densely clothed with vegetation. Many of the spurs or broken segments of ranges thus formed abut steeply upon the Black Sea, so that this littoral region is on the whole very rugged and not readily accessible, especially as the general elevations are considerable. The seaward flanking ranges run up to 4000 ft. and more, and in many places shoot out cliffs which overhang the coast some 2000-3000 ft. sheer, while the main range gradually ascends to 10,000-12,000 ft. as it advances eastwards, the principal peaks being Fisht (8040 ft.), Oshten (9210 ft.), Shuguz (10,640 ft.), and Psysh (12,425 ft.). And whereas the main range is built up of hard eruptive or crystalline rocks, the subsidiary chains are composed of softer (Cretaceous and Tertiary) laminated formations, which easily become disintegrated and dislocated . The snow-line runs here at about 9000 ft. on the loftiest summits, and east of Oshten the crest of the main range is capped with perpetual snow and carries many hanging glaciers, while larger glaciers creep down the principal valleys . The passes lie at relatively great altitudes and are few in number, so that although the northern versants of the various ranges all have a tolerably gentle slope, communication between the Black Sea and the valley of the Kuban, and the low steppe country beyond, is the reverse of easy. The more important passes, proceeding from west to east, are Pshekh (5435 ft.) west of Oshten, and Shetlib (6060 ft.) east of Oshten, Pseashka (688o ft.) east of Shuguz, Sanchar (7990 ft.) west of Psysh; and between the last-named mountain and Elbruz, facilitating communication between Sukhum-Kaleh (and the coast as far as Poti) and the upper valley of the Kuban, are the passes of Marukh (11,500 ft.), Klukhor (9450 ft.) and Nakhar (9615 ft.).

The southern exposure of this littoral region, the shelter afforded against the bitter winds of the north by the lofty Caucasus range, and the copious rainfall all combine to foster a luxuriant and abundant vegetation. The most distinguishing feature of the flora of this region is the predominance of arborescent growths; forests cover in fact 56% of the area, and are not only dense but laced together with climbing and twining plants. The commonest species of trees are such as grow in central Europe, namely, ash, fir, pine, beech, acacia, maple, birch, box, chestnut, laurel, holm-oak, poplar, elm, lime, yew, elder, willow, oak. The common box is especially prevalent, but the preponderating species are Coniferae, including the Caucasian species Pinus halepensis and P. insignis. The commonest firs are Abies nordmannia and A. orientalis. There are two native oaks, Quercus ponticus and Q. sessiliftora. A great variety of shrubs grow on these slopes of the western Caucasus, chiefly the following species, several of which are indigenous—Rhododendron ponticum, Azalea pantica, Aristotelia maqui, Agave americana, Cephalaria tatarica, Cotoneaster pyracantha, Citrus aurantium, Diospyros ebenum, Ficus carica, Illicium anisatum, Ligustrum caucasicum, Punica granatum, Philadel phus coronarius, Pyrus salicifolia, Rhus cotinus and six species of Viburnum. Aquatic plants thrive excellently and occur in great variety. The following purely Caucasian species also grow on the coast-five species of spearwort, three of saxifrage, Aster caucasica, Dioscorea caucasica, Echinops raddeanus, Hedera colchica, Hellebores caucasica and Peucedanum caucasicum. Here too are found many of the more beautiful open-air flowering plants of a shrubby character, e.g. magnolia, azalea, camellia, begonia and paulownia. Among the cultivated trees and shrubs the most valuable economically are the vine, peach, pomegranate, fig, olive (up to 1500 ft. above sea-level), chestnut, apricot, apple, pear, plum, cherry, melon, tea (on the coast between Sukhum-Kaleh and Batum), maize (yielding the staple food of the inhabitants), wheat (up to 6000 ft.), potatoes, peas, currants, cotton, rice, colza and tobacco. Before the Russian conquest the native inhabitants of this region were Kabardians, Circassians (Adigheh) and Abkhasians also a Circassian race But half a million of these th the yoke of Christian Russia, emigrated into Turkish territory between 1864 and 1878, and the country where they had lived remained for the most part unoccupied until after the beginning of the 20th century. Then, however, the Russian government held out inducements to settlers, and these have been responded to by Russians, Greeks, Armenians and Rumanians, but the process of repeopling the long deserted territory is slow and difficult. The coast-line is remarkably regular, there being no deep bays and few seaports. The best accommodation that these latter afford consists of more or less open roadsteads, e.g . Novo-rossiysk, Gelenjik, Anapa, Sukhum-Kaleh, Poti and Batum.

Along the coast a string of summer bathing resorts is springing up similar to those that dot the south-east coast of the Crimea . The most promising of these little seaside places are Anapa, Gelenjik and Gagry.

The crest of the main range runs continuously at an altitude exceeding l0,000 ft., but even it is surpassed in elevation by the secondary range to the north, the Bokovoi Khrebet. These two ranges are connected by more than half a dozen short trans-verse spurs or necks, inclosing as many cirques or high cauldron glens. Besides the Bokovoi Khrebet several other short subsidiary ranges branch off from the main range at acute angles, lifting up high montane glens between them; for instance, the two ranges in Svanetia, which divide, the one the river (glen) Ingur from the river (glen) Tskhenis-Tskhali, and the other the river (glen) Tskhenis-Tskhali from the rivers (glens) Lechkhum and Racha. Down all these glens glacier streams descend, until they find an opportunity to pierce through the flanking ranges, which they do in deep and picturesque gorges, and then race down the northern slopes of the mountains to enter the Terek or the Kuban, or down the southern versant to join the Rion or the Kura . Amongst all these high glens there is a remark-able absence of lakes and waterfalls; nor are there down in the lower valleys at the foot bf the mountains, as one would naturally expect in a region so extensively glaciated, any sheets of water corresponding to the Swiss lakes. In this section of the Caucasus the loftiest peaks do not as a rule rise on the main range, but in many cases on the short spurs that link it with the Bokovoi Khrebet and other subsidiary ranges.

"The central chain of the Caucasus," writes Mr Douglas W . Freshfield,[1] "consists of a number of short parallel or curved horse-shoe rides, crowned with rocky peaks and enclosing basins filled by the névés of great glaciers . . . On either side of the main chain the same succession is repeated, with one important difference . On the north the schists come first, sometimes rising into peaks and ridges in a state of ruin . . but more often worn to rolling downs; then the limestone range—writing-desk mountains that turn their steep fronts to the central snows; lastly low Cretaceous foothills, that sink softly into the steppe . But on the south side the crystal-line rocks are succeeded by a broad belt of slates, as to the age of which the evidence is at present conflicting and the opinion of geologists divided. East of Adai-khokh, by what seems a strange freak of nature, the granitic [main] range is rent over and over again to its base by gorges, the watershed being transferred to the parallel chain of clay slates . . . which has followed it from the Black Sea, attaining on its way the height of 13,400 ft. in the Laila, and limiting the great parallel basins of the Rion, Ingur and Skenis Shalt [ = Tskhenis-Tskhali] ..." " At the base of the central core of the chain spread (to the north) broad, smooth, grassy downs, the pastures of the Turk and the Ossete Their ridges attain to 9000 to 10,000 ft. They are composed of friable crystalline schists . . Beyond these schists rises a broken wall of limestone, cleft to the base by gorges, through which flow the mountain torrents, and capped by pale precipitous battlements, which face the central chain at a height of 11,000 to 12,000 ft. Beyond, again, lies a broad furrow, or 'longitudinal fold,' as geologists call it, parallel to the ridges, and then rises the last elevation, a belt of low calcareous hills, on which, here and there among the waves of beech forest, purple or blue with distance, a white cliff retains its local colour and shines like a patch of fresh snow. Beyond, once more beyond, spreads the Scythian steppe, not the dead level of Lombardy, but an expanse of long low modulations, which would be reckoned hills in our home counties, seamed by long shining ribbons, which mark the courses of the tributaries of the Terek . . Southwards too, immediately under the snows, we find 'crystalline sclusts,' smooth grassy heights, separated by shallow trenches, which form the lesser undulations of the three basins, the drei Langenhochthäler Imeritiens of Dr Radde. These basins or 'longitudinal folds' are enclosed on the south by the long high ridge of dark slates, which extends parallel to the crystalline [main) chain from the neighbourhood of Sukhum-Kale to the Krestovaya Gora [pass of Darial.] Behind this slate crest spreads a confused multitude of hills, Jurassic and Cretaceous in their formation . . . . Their outer edge, distant some 30 to 4om. from the snows, is marked by a limestone belt, lower and less continuous than that on the north, which frames the gorges of the Rion, and rises in the Kuamli (652 ft.) and Nakarala 4774 ft.) near Kutais, its best known elevations."[2] It may be added that, south of the central watershed, the strata, both Mesozoic and Palaeozoic, are compressed, crumpled, faulted and frequently over-folded, with their apices pointing to the south .

As a rule the snow-line runs at 9500 to 10,000 ft. on the northern face and 1000 ft. higher on the southern face. It is estimated that there are in all over nine hundred glaciers in this section of the range, and although they often rival those of the Alps in size, they do not descend generally to such low altitudes as the latter. The best known are the Bezingi or Ullu, between Dykh-tau and Janga-tau, 10½ m. long, covering an area of 31 sq. m., and descending to 6535 ft. above sea-level; Leksyr, situated south of Adyr-su-bashi, 7½ m. long, 19 sq. m. in area, and creeping down to as low as 5690 ft., this being the lowest point to which any glacier descends on the south side of the range; Tseya or Zea, descending 6 m. from the Adai-khokh to an altitude of 6730 ft.; Karagom, from the same mountain, 9½ m. long, 14 sq. m. in area and reaching down to 5790 ft., the lowest on the north side; Dyevdorak or Devdorak, from Kasbek, 24 m. long, its lower end at 7530 ft.; Khaldeh or Geresho 41 m. long, from Shkara and Janga-tau; Tuyber from Tetnuld, 64 m. long, area 21 sq. m., and reaching down to 6565 ft.; Tsanner or Zanner, the same length and the same area, but stopping short 240 ft. higher, likewise given off by Tetnuld; while between that peak, Adish and Gestola originates the Adish or Lardkhat glacier, 5 M. long and terminating at 7450 ft. The total area covered by glaciers in the central Caucasus is estimated at 625 to 65o sq. m., the longest being the Maliev on Kasbek, 36 m. long; but according to the investigations of M . Rossikov several of the. largest glaciers are shrinking or retreating, the Tseya at the rate of something like 40-45 ft. per annum.

It is in this section that the entire mountain system is narrowest, and here it is that (apart from the "gate" at Derbent close beside the Caspian) the principal means of communication exist between north and south, between the steppes of southern Russia and the highlands of Armenia and Asia Minor . These means of communication are the passes of Darial and Mamison . Over the former, which lies immediately east of Kasbek, ' runs the Georgian military road (made 1811-1864) from Vladikavkaz to Tiflis, cutting through the mountains by a gorge (8 m. long) of singular beauty, shut in by precipitous mountain walls nearly 6000 ft. high, and so narrow that there is only just room for the carriage-road and the brawling river Terek side by side. The pass by which this road crosses the main range, farther south, is known as the Krestovaya Gora (Mountain of the Cross) and lies 7805 ft. above sea-level. The Mamison Pass, over which runs the Ossetic military road (made passable for vehicles in 1889) from the Terek (below Vladikavkaz) to Kutais in the valley of the Rion, skirting the eastern foot of the Adai-khokh, lies at an altitude of 9270 ft. and is situated a little south of the main range. Scarce any of the remaining passes in this west-central region are better than mountain paths; horses can traverse the best of them only during a few weeks in the height of summer. They mostly range at altitudes of 9000 - 12,500 ft., and between the pass of Nakhar in the west and that of Mamison in the east there is not a single pass below 10,000 ft. The best known in this section are the three Baksan passes of Chiper (10,800 and 10,720 ft.), Bassa (9950 ft.) and Donguz-orun (10,490 ft.), south of Elbruz; those of Becho (11,070 ft.), Akh-su (12,465 ft.), Bak (10,220 ft.), Adyr-su (12,305 ft.) and Bezingi (10,090 ft.), between Elbruz and Dykh-tau; and those of Shari-vizk (11,560 ft.), Edena, Pasis-mta or Godivizk (11,270 ft.), Shtulu-vizk (10,860 ft.), Fytnargyn (11,130 ft.), between Dykh-tau and Adai-khokh; the Bakh-fandak (9570 ft.), between Adai-khohk and Kasbek; and the two Karaul passes (11,680 and 11,270 ft.) and Gurdzi-vizk (10,970 ft.), connecting the valley of the Urukh with that of the Rion. The most frequented pass in Svanetia is that of Latpari (9260 ft.), situated in the first of the southern subsidiary ranges mentioned above, and thus connecting the valley of the Ingur with the valley of the Tskhenis-Tskhali.

In this section of the range again the southern slopes are clothed with vegetation of remarkable luxuriance and richness, more especially in the region of Svanetia (42°-43°E.) . Not only are the plants bigger than they grow in the Alps, but the blossoms are more abundant . Here again forests of Coniferae predominate, especially on the northern and eastern slopes; and the other distinguishing features of the flora are gigantic male ferns (Aspidium filix-mas), Paris incompleta (a member of the Trilliaceae), Usnea or tree-moss, box, holly (Ilex agui folium), Lilium monadelphum and many of the familiar herbaceous plants which flower in English gardens, though here they grow to an altogether extraordinary size— "monkshoods, Cephalaria, Mulgedia and groundsels, among which men on horseback might play at hide and seek without stooping " (E . Levier) . Other prominent species are Campanula, Pyrethrum, aconite, Cephaglis, speedwell, Alchemilla sericea, Centaurea macrocephala, Primula grandis and a species of primrose. And the great height (13,000 ft.) at which the flowering plants blossom is not less remarkable than the great beauty and abundance of the flowers. Species which grow on both the northern and the southern slopes ascend, 2000 ft. higher on the latter than on the former . Walnuts grow up to an altitude of 5400 ft., the vine and mulberry up to 3250 ft., the lime and ash to 4000 ft. The forests extend to the upper end of the limestone gorges. Above that the crystalline schists are bare of tree vegetation . The upper limit of arborescent vegetation is considered to run at 7000-7500 ft., of shrubs such as rhododendrons at 8500 ft., and of pasture-lands up to 9000 ft. The principal cultivated varieties of plants in this section are wheat, rye, oats, barley, beans, millet and tobacco.

In this sub-section, which stretches from Kasbek and the Darial gorge eastwards to the Baba-dagh in 48° 25' E., a distance of 230 m., the Caucasus attains its greatest breadth. For the whole of that distance the main range keeps at an average elevation of 10,000 ft., though the peaks in many instances tower up 2000 to nearly 5000 ft. higher, the altitudes increasing towards the east. As the main range approaches the Caspian its granite core gradually disappears, giving place to Palaeozoic schists, which spread down both the northern and the southern slopes. The glaciers too decrease in the same proportion both in magnitude and in extent. Here the principal peaks, again found for the most part on the spurs and subsidiary ranges, are the Tsmiakom-khokh (13,570 ft.), Shan-tau (14,530 ft.), Kidenais-magali (13,840 ft.), Zilga-khokh (12,645 ft.), Zikari (12,565 ft.), Choukhi (12,110 ft.), Julti-dagh (12,430 ft.), Alakhun-dagh (12,690 ft.) and Maghi-dagh (12,445 ft.). On the main range itself stand Borbalo (10,175 ft.), Great Shavi-kildeh (12,325 ft.), Murov (11,110 ft.), Ansal (11,740 ft.), Ginor-roso (11,120 ft.), while farther east come Trfan-dagh (13,765 ft.) and Bazardyuz or Kichen (14,727 ft.). In the same direction, but again outside the main range, lie Shah-dagh (13,955 ft.), Shalbuz (13,675 ft.) and Malkamud (12,750 ft.).

But the most noteworthy feature of this section is the broad highland region of Daghestan, which flanks the main range on the north, and sinks down both eastwards to the Black Sea and northwards to the valley of the Terek. On the north-west this rugged highland region is well defined by the distinctive trans-verse ridge of Andi, which to the east of Kasbek strikes off from the Caucasus range almost at right angles. The rest of the Daghestan region consists of a series of roughly parallel folds, of Jurassic or Cretaceous age, ranging in altitudes from 7500 up to 12,500 ft., separated from one another by deep gorge-like river glens which cut it up into a number of arid, treeless plateaus which have something of the appearance of independent ranges, or rather elongated tablelands of a mountainous character . The most prominent of these tablelands is Bash-lam, which stretches east and west between the Chanti Argun and the Andian Koisu, both tributaries of the Terek.

Upon it rise the conspicuous peaks of Tebulos-mta (14,775 ft.), Tugo-rota (13,795 ft.), Komito-tavi or Kachu (14,010 ft.), Donos-mta (13,560 ft.), Diklos-mta (13,740 ft.), Kvavlos-mta or Kolos-mta (13,080 ft.), Motshekh-tsferi (13,140 ft.) and Galavanas-tsferi (13,260 ft.). Farther east come the Bogos tableland, stretching from south-south-west to east-north-east between the Andian Koisu and the Avarian Koisu and rising to over 13,400 ft. in several peaks, e.g . Antshovala(13,440 ft.), Botshokh-meer (13,515 ft.), Kosara-ku (13,420 ft.) and Addala-shuogchol-meer (13,580 ft.); and the Dyulty tableland, reaching 12,400 ft. between the Kara Koisu and the Kazikumukh Koisu. On some of these peaks again there is a considerable amount of glaciation, more particularly on the slopes of Diklos-mta, where the glaciers descend to 7700 ft. on the north side and to 8350 ft. on the south side. In this section of the Caucasus the passes run somewhat lower than those between Elbruz and Kasbek, though still at appreciable heights, fully equal to those that lead up from the Black Sea to the valley of the Kuban in the western section of the range. The best known are the Krestovaya Gora (7805 ft.) on the Georgian military road, south of Darial; Kodor (9300 ft.) and Satskheni, leading up from Telav in the upper valley of the Alazan; and Gudur (10,120 ft.) and Salavat (9280 ft.), carrying the Akhty military road from the valley of the Samur up past the Shah-dagh and the Bazar-dyusi to the valley of the Alazan . The flora of this section bears a general resemblance to that farther west. Ample details will be found in Dr G . Radde's (1831–1903) monographs on Daghestan, quoted at the end of the present article.

The Eastern Section of the Caucasus gradually dies away east of Baba-dagh (11,930 ft.) towards the Caspian, terminating finally in the peninsula of Apsheron . It is, however, continued under the waters of the Caspian, as stated in the article on that sea, and reappears on its eastern side in the Kopet-dagh, which skirts the north-east frontier of Persia. In this section of the Caucasus no peak exceeds 9000 ft. in altitude and the crest of the main range retains no snow. The most frequented pass, that of Alty-agach, necessitates a climb of not more than 4355 ft.

Between the northern and the southern sides of the range there is quite as great a difference in climate, productions and scenery as there is between the Swiss and the Italian sides of the Alps . In the south-western valleys and on the south-western slopes of the Caucasus, where a heavy rainfall is combined with a warm temperature, magnificent forests clothe the mountain-sides and dip their skirts into the waters of the Black Sea. There not only the littoral from (say) Sukhum-Kaleh to Batum but the inland parts of the basin of the Rion will bear comparison with any of the provinces of Italy in point of fertility, and in richness and variety of products . But farther inland, upon proceeding eastwards towards Tiflis, a great change becomes noticeable on the other side of the transverse ridge of the Suram or Meskes mountains. Arid upland plains and parched hillsides take the place of the rich verdure and luxuriant arborescent growth of Imeretia, Svanetia and Mingrelia, the districts which occupy the valleys of the Ingur and Rion and the tributaries of the latter. A very similar change likewise becomes noticeable in the higher regions of the Caucasus Mountains upon proceeding north of the pass of Mamison, which separates the head-waters of the Rion from those of the Ardon, an important tributary of the Terek. The valleys of the two streams last mentioned, and of others that flow in the same direction, are almost wholly destitute of trees, but where the bare rock does not prevail, the mountain slopes are carpeted with grass. Fresh-field's description of the valley of the Terek above Kasbek will apply pretty generally to all the valleys that descend on that face of the range: " treeless valleys, bold rocks, slopes of forbidding steepness (even to eyes accustomed to those of the Alps), and stonebuilt villages, scarcely distinguishable from the neighbouring crags." But, austere and unattractive though these valleys are, the same epithets cannot be applied to the deep gorges by which in most cases the streams make their escape through the northern subsidiary range . These defiles are declared to be superior in grandeur to anything of the kind in the Alps . That of Darial (the Terek) is fairly well known, but those of the Cherek and the Urukh, farther west, are stated to be still more magnificent. And not only do the snow-clad ranges and the ice-panoplied peaks which tower up above them surpass the loftiest summits of the Alps in altitude; they also in many cases excel them in boldness and picturesqueness of outline, and equal the most difficult of them in steepness and relative inaccessibility.

Nearly all the larger rivers of Caucasia have their sources in the central parts of the Caucasus range. The short, steep, torrential streams of Mdzimta, Pzou, Bzyb and Kodor drain the country west of Elbruz. The Ingur, Tskhenis-Tskhali, Rion and its tributaries (e.g. the Kvirila) are longer, but also in part torrential; they drain the great glacier region between Elbruz and Kasbek. The Rion is the Phasis of the ancients and flows through the classic land of Colchis, associated with the legends of Medea and the Argonauts. The Lyakhva and Aragva, tributaries of the Kura, carry off the waters of the main range south of Kasbek, and other tributaries, such as the Yora and the Alazan, collect the surplus drainage of the main Caucasus range farther east. The other large river of this, region, the Aras, has its sources, not in the Caucasus range, but on the Armenian highlands a long way south-west of Ararat. The rivers which go down from the central Caucasus northwards have considerably longer courses than those on the south side of the range, partly as a consequence of the gentler versant and partly also because of the great distances to which the steppes extend across which they make their way to the sea. The most important of these are the Kuban and the Terek; but it is the latter that picks up most of the streams which have their sources among the central glaciers, e.g. the Malka, Baksan, Chegem, Cherek, Urukh, Ardon, all confined to deep narrow glens until they quit the mountains. The Kuma, which alone pursues an independent course through the steppes, farther north than the Terek, has its sources, not in the main ranges of the Caucasus, but in an outlying group of mountains near Pyatigorsk, the highest summit of which, Besh-tau, does not exceed 4600 ft. But its waters become absorbed in the sands of the desert steppes before they reach the Caspian. Of the streams that carve into chequers the elevated plateau or highland region of Daghestan four are known by the common name of. the Koisu, being distinguished inter se as the Andian Koisu, the Avarian Koisu, the Kara Koisu and the Kazikumukh Koisu, which all unite to form the Sulak. The only other stream deserving of mention in this province is the Samur. Both rivers discharge their waters into the Caspian; as also does the Zumgail, a small stream which drains the eastern extremity of the Caucasus range in the government of Baku.

Ancient, but now extinct, volcanic upheavals are pretty common at the intersections of the main range with the transverse ranges; of these the most noteworthy are Elbruz and Kasbek . The town of Shemakha, near the eastern end of the system, was the scene of volcanic outbreaks as late as 1859, 1872 and 1902; while in the adjacent peninsula of Apsheron mud volcanoes exist in large numbers. All along the northern foot of the system hot mineral springs gush out at various places, such as Pyatigorsk, Zhelesnovodsk, Essentuki and Kislovodsk; and the series is continued along the north-eastern foot of the highlands of Daghestan, e.g. Isti-su, Eskiendery, Akhta. In this connexion it may also be mentioned that similar evidences of volcanic activity characterize the northern border of the Armenian highlands on the southern side of the Rion-Kura depression, in the mountains of Ararat, Alagoz, Akmangan, Samsar, Godoreby, Great and Little Abull, and in the mineral springs of Borzhom, Abbas-tuman, Sleptzov, Mikhailovsk and Tiflis.

The general structure of the Caucasus is comparatively simple. The strata are folded so as to form a fan. In the centre of the fan lies a band of crystalline rocks which disappears towards the east. Beneath it, on both sides, plunge the strongly folded Palaeozoic and Jurassic schists. On the northern flank the folded beds are followed by a zone of Jurassic and Cretaceous beds which rapidly assume a gentle inclination towards the plain. On the south the corresponding zone is affected by numerous secondary folds which involve the Sarmatian or Upper Miocene deposits. In the eastern part of the chain the structure is somewhat modified. The crystalline band is lost. The northern Mesozoic zone is very much broader, and is thrown into simple folds like those of the Jura. The southern Mesozoic zone is absent, and the Palaeozoic zone sinks abruptly in a series of faulted steps to the plain of the Kura, beneath which no doubt the continuation of the Mesozoic zone is concealed.

The geological sequence begins with the granite and schists of the central zone, which form a band extending from Fisht on the west to a point some distance beyond Kasbek on the east. Then follow the Palaeozoic schists and slates. Fossils are extremely rare in these beds; Buthotrephis has long been known, and doubtful traces of Calamites and ferns have been found, but it was not until 1897 that undoubted Palaeozoic fossils were obtained. They appear to indicate a Devonian age. Upon the Palaeozoic beds rest a series of Mesozoic deposits, beginning with the Lias and ending with the Upper Cretaceous. Whether the series is continuous or not is a matter of controversy. F. Loewinson-Lessing states that there is a more or less marked discordance between the Lias and the Upper Jurassic and between the latter and the Cretaceous; E. Fournier asserts that there exists a very strongly marked unconformity at the base of the Tithonian, and other writers have expressed other views. In general the Upper Jurassic beds are much more calcareous on the north flank of the chain than they are on the south. The Mesozoic beds are followed by the Tertiary deposits, which on the north are nearly horizontal but on the south are in part included in the folds—the Eocene and Miocene being folded, while the later beds, though sometimes elevated, are not affected by the folding. The final folding of the chain undoubtedly occurred at the close of the Miocene period. That there were earlier periods of folding is almost equally certain, but there is considerable difference of opinion as to their dates. The difference in character of the Jurassic beds on the two sides of the chain appears to indicate that a ridge existed Quaternary Cretaceous Tertiary Jurassic in that period. The last phase in the history of the Caucasus was marked by the growth of the great volcanoes of Elbruz and Kasbek, which stand upon the old rocks of the central zone, and by the outflow of sheets of lava upon the sides of the chain. The cones themselves are composed largely of acid andesites, but many of the lavas are augite andesites and basalts. There seem to have been two periods of eruption, and as some of the lavas have flowed over Quaternary gravels, the latest outbursts must have been of very recent date.

Near the northern foot of the Caucasus, especially in the neighbourhood of the hot mineral springs of Pyatigorsk, a group of hills of igneous rocks rises above the plain. They are laccolites of trachytic rock, and raised the Tertiary beds above them in the form of blisters . Subsequent denudation has removed the sedimentary covering and exposed the igneous core.